The present disclosure generally relates to systems and methods for controlling cerebrospinal fluid in a subject's ventricular system and, more particularly, to systems and methods that control the cerebrospinal fluid such that the average intracranial pressure is maintained within a specific range.
Hydrocephalus is a disorder in which a subject's body produces cerebrospinal fluid (CSF) at a rate faster than the venous system absorbs the fluid. The increased intracranial pressure (ICP) caused by the excess fluid can lead to a number of uncomfortable and potentially dangerous neurological symptoms, such as headaches, cerebral edema, and intracranial hematoma.
Traditional treatment for hydrocephalus involves connecting a drainage shunt between a subject's ventricular system, in which CSF accumulates, and another body cavity, such as the peritoneal cavity. As such, CSF drains from the subject's ventricular system and is absorbed by tissue proximate the shunt outlet.
In some cases, unfortunately, drainage shunts can lead to slit ventricle syndrome. With this disorder, the shunt over-drains the CSF in the ventricular system. The reduced amount of CSF in the ventricular system results in low ICP, which in turn causes ventricular ependymal tissue to collapse around the shunt inlet. The low ICP can result in debilitating headache and, in more severe cases, dural hemorrhage. The collapse of ventricular ependymal tissue around the shunt inlet can also block entry of CSF into the shunt system. Over time, such shunt obstruction can lead to a rise in ICP. With repeated cycles of low and high ICP, complete blockage of the shunt inlet can occur, leading to potentially life-threatening shunt failure. In this case, the shunt must be urgently replaced.
In an attempt to address slit ventricle syndrome and CSF over-drainage, some shunts include a valve that inhibits continuous CSF drainage and attempts to maintain generally constant ICP. In particular, such valves typically prevent CSF drainage from the ventricular system unless a pressure differential threshold across the valve is exceeded. Unfortunately, some subjects using these shunt/valve systems nevertheless develop slit ventricle syndrome, for reasons that are, generally, unclear.
Research has lead some to deduce that, in some cases, subjects develop slit ventricle syndrome even when using the above shunt/valve systems due to the varying effect of gravity on CSF pressure as the subject changes orientation (e.g., as the subject moves from a supine to an upright orientation or vice versa). In contrast to when a subject lies in a supine orientation, the weight of the CSF in the ventricular system and in the shunt itself can act on the valve when the patient is upright. This load on the valve leads to inappropriate actuation, once again causing CSF over-drainage and decreased ICP. In some shunt/valve systems, the valve is repositioned and the path of the shunt passageway is modified to reduce the amount of CSF weight that the valve resists. In these cases, however, the valve is still subjected to inappropriate actuation due to siphon effects, which arise due to the weight of CSF in the shunt tubing itself.
Some shunt systems include structures that compensate for such gravitational pressure effects, but even in these cases, some subjects nevertheless experience CSF over-drainage and develop slit ventricle syndrome. Moreover, drainage shunts that incorporate a series of valves or structures for compensating for gravitational pressure effects, empirically, seem to be able to delay, but not prevent, the development of slit ventricle syndrome. When gravitational effects are compensated for, research has yet to definitively explain occurrences of slit ventricle syndrome.
Considering the drawbacks of previous hydrocephalus treatment stents, what is needed in the art is a system for controlling cerebrospinal fluid in a subject's ventricular system in a manner that inhibits CSF over-drainage.